Structural characterization of a fluorescein hydrazone molecular switch with application towards logic gates

Abstract

A fluorescein acylhydrazone (2) as well as its metal complexes with Zn2+, Ni2+ and Cu2+ ions were synthesized and characterized by means of NMR (1H, 13C and 2D experiments), UV-Vis, fluorescence spectroscopy, FT-IR and single crystal X-Ray diffraction. The compound crystallizes in Pī triclinic space group, with two fluorescein acylhydrazone (2) conformers and one water molecule per symmetric unit. The fluorescein acylhydrazone (2) and metal derivates were analysed by cyclic voltammetry, finding a relation between the shifting in their redox potential with the quenching of fluorescence. Emission and UV-Vis absorption logic gates were fabricated based on the metal ion binding of 2 and its behaviour at different pH values. Compound 2 exhibited “on-off” behaviour in the fluorescence emission with the addition of triethylamine (TEA) this effect is highly enhanced by the joint addition of Zn2+. Conversely, the fluorescence is highly quenched by the addition of trifluoroacetic acid (TFA) or Ni2+ ions allowing to fabricate a AND gate using TEA and Zn2+ as inputs, and a INHIBIT gate with the addition of TFA or Ni2+, both using the fluorescence emission as outputs. The addition of Cu2+ resulted in a fluorescence emission at 525 nm that is red shifted with the addition of TEA. This behaviour allowed us to construct a XOR gate with the fluorescence emission at 525 nm as output, and the addition of Cu2+ and TEA as inputs. The absorption in the visible region was used to create AND gates with the addition of Cu2+ ions and TEA, or Ni2+and TEA as inputs. The INH, AND, XOR gates were manipulated by the controlled addition of different metal cations, TEA and TFA as inputs, and fluorescence emission and visible absorption as outputs allowing us to create three different combinatorial circuits in which we want to highlight a new molecular “HALF-ADDER”.